Inorganic or hybrid inorganic/organic layers have been used in thin films for electrical, packaging and decorative applications. These layers can provide desired properties such as mechanical strength, thermal resistance, chemical resistance, abrasion resistance, moisture barriers, and oxygen barriers.
Inorganic or hybrid films can be prepared by a variety of production methods. These methods include liquid coating techniques such as solution coating, roll coating, dip coating, spray coating, spin coating, and dry coating techniques such as Chemical Vapor Deposition (CVD), Plasma Enhanced Chemical Vapor Deposition (PECVD), sputtering and vacuum processes for thermal evaporation of solid materials. Each of these methods has limitations.
Chemical vapor deposition methods (CVD and PECVD) form vaporized metal alkoxide precursors that undergo a reaction, when adsorbed on a substrate, to form inorganic coatings. These processes are limited to low deposition rates (and consequently low line speeds), and make inefficient use of the alkoxide precursor (much of the alkoxide vapor is not incorporated into the coating). The CVD process also requires high substrate temperatures, often in the range of 300-500° C., which may not be suitable for polymer substrates.
Sputtering has also been used to form metal oxide layers. This process is characterized by slow deposition rates allowing web speeds of just a few feet/min. Another characteristic of the sputtering process is its very low material utilization, because a major part of the solid sputtering target material does not become incorporated in the coating. The slow deposition rate, coupled with the high equipment cost, low utilization of materials, and very high energy consumption, makes it expensive to manufacture films by sputtering.
Vacuum processes such as thermal evaporation of solid materials (e.g., resistive heating or electron-beam (e-beam) heating) also provide low metal oxide deposition rates. Thermal evaporation is difficult to scale up for roll wide web applications requiring very uniform coatings (e.g., optical coatings) and can require substrate heating to obtain quality coatings. Additionally, evaporation/sublimation processes can require ion-assist, which is generally limited to small areas, to improve the coating quality.
There remains a need for a method to prepare inorganic or hybrid inorganic/organic barrier films on polymeric substrates that can be performed rapidly and at low cost.